Would like for SimpleEmailMessage to include Tags

[charles-circulo]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I find a struct that solves 99% of my problems, but then falls just short.

Describe the solution you'd like
When processing SES events in golang, I'd like for the SimpleEmailMessage struct to include Tags.

Describe alternatives you've considered
I will need to print out an example event and take it to a golang JSON parser to build a custom struct.

Additional context
Just update to this? I can handle the type conversion/parsing from there.

type SimpleEmailMessage struct {
	CommonHeaders    SimpleEmailCommonHeaders `json:"commonHeaders"`
	Source           string                   `json:"source"`
	Timestamp        time.Time                `json:"timestamp"`
	Destination      []string                 `json:"destination"`
	Headers          []SimpleEmailHeader      `json:"headers"`
	HeadersTruncated bool                     `json:"headersTruncated"`
	MessageID        string                   `json:"messageId"`
	Tags             map[string][]string      `json:"tags"`
}

[bmoffatt]

#450 needed re-work, as this tags field is relevant in SES-via-SNS, which is an entirely different event struct this project doesn't have right now.

👍 Suggest putting the new types & tests in a new file ses_via_sns.go/ses_via_sns_test.go, to help with the self documentation that this is a different integration than the direct SES -> Lambda email receipt integration.

The closer similar test data to emulate type I think is cloudwatch-alarm-sns-payload-multiple-metrics.json, such that the send, bounce, click, etc.., are stringified JSON inside the SNS Message field